Police have been attacked with petrol bombs after finding a suspicious object in the Creggan area of Londonderry.
About 80 officers had been searching for bomb-making equipment on Monday, targeting dissident republicans in the Northern Irish city.
It followed the discovery of an improvised explosive device in Strabane during the weekend which has been linked to the New IRA.
Police said the mortar was near a family home and was aimed at the local police station.
In Derry on Monday, officers were targeted while carrying out searches and about 15 homes were evacuated to keep residents safe, police added.
Police Service of Northern Ireland Assistant Chief Constable Mark Hamilton described the operation around the suspicious object as “complex”.
He added: “This is a complex operation which is expected to continue throughout the night and we have advised those residents who have left their homes to make alternative arrangements.
“We recognise the upheaval this has caused and we are grateful for their co-operation and understanding.
“The focus of this operation is ensuring the people of Creggan are safe however it is concerning to see significant numbers of young people on the streets, late into the night, throwing petrol bombs and other missiles at officers in the area.
“The reality is this type of disorder contributes to the complexity of the policing operation and presents a real risk of injury to those involved.
“Already we have seen two incidents this evening where young people have sustained burn injuries as result of engaging in disorder.
“I would reiterate our appeal for those young people to return home and remove themselves from the situation.
“We are grateful for the support of community representatives in helping to reduce tensions and providing space for officers to carry out the necessary work to ensure this object does not present a risk to the people of Creggan.”
Sinn Fein Assembly member Karen Mullan said: “There is absolutely no justification for the actions which serve no purpose other than to put people at risk of serious harm and make the situation worse for local residents trying to get on with their lives, and they should stop now.”
SDLP leader Colum Eastwood added: “The brutal and sustained attack that officers have come under while trying to make our community safe is disgusting. Young people in this community are being manipulated and are risking their futures as a result. I would urge parents to contact their children and take them out of harm’s way.
“People in this community will not be held to ransom by those who want to hold us all back.”
Meanwhile, a 33-year-old man arrested in connection with the improvised explosive device found during the weekend has been released.
Police have been attacked with petrol bombs after finding a suspicious object in the Creggan area of Londonderry. About 80 officers had been searching for bomb-making equipment on Monday, targeting dissident republicans in the Northern Irish city. It followed the discovery of an improvised explosive device in Strabane during the weekend which has been linked to the New IRA.